Microwave synthesis of metallosilicate zeolites with fibrous morphology.
In this paper, we report syntheses of silicalite (Si-MFI) zeolite crystals with tetravalent metal ions incorporated to synthesize metallosilicalite (M-MFI; M = Sn, Zr, Sn/Zr, Ti/Zr) zeolite crystals by using microwave irradiation reactions. Beta-Diketonate (acetylacetone) was used as a chelating ligand of the metal precursors, in order to reduce their hydrolysis rates and, therefore, to enhance framework incorporation of each metal in the syntheses of M-MFI zeolites. The zeolite crystals formed show puck-like morphology, and these crystals are stacked to form fibers with the degree of self-assembly varied depending on the nature of the tetravalent metal ion used. Importantly, the self-assembly of the zeolite crystals and the resultant fibrous morphology are observed only when the substituting metal ions are present. Powder X-ray diffraction, infrared and ultraviolet diffuse reflectance spectroscopic data all indicate that Sn and Ti atoms are well substituted for Si, but Zr is not well incorporated in the resulting MFI crystals. These results are discussed in terms of the ionic sizes and bulk dielectric constants of the corresponding metal oxides of the substituting metal ions.